In the recent report of the Task Group to establish a Global Stratotype Section and Point (GSSP) at the K a s i m o v i a n-G z h elian boundary (Villa and Task Group, 2005) and in a series of recent publications (H e c kel et al., 2005; C h e r n y k h, 2005; M e n n i n g et al., 2006; etc.), the conodont species Streptognathodus simulator Ellison, 1941 (regarded as Idiognathodus by some authors), has been proposed as the best index-fossil for the definition of the base of the global

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The dynamics of changes in individual electrical activity rhythms in the premotor, sensorimotor, and temporal-parietal areas of the cortex in both hemispheres were studied in chronic experiments in rabbits during sequential sessions of "animal hypnosis." These experiments showed that during the first session of "animal hypnosis," significant changes in electrical activity occurred only in the premotor area of the cortex of the right hemisphere, where there were increases in spectral power in the delta-1 and delta-2 ranges and decreases in spectral power in other ranges of electrical activity. Subsequent sessions of "animal hypnosis" formed increasing changes in electrical activity, which were particularly marked in cortical areas in the right hemisphere. Significant changes in spectral power in the delta and theta ranges of electrical activity in cortical areas did not arise at the beginning of the hypnotic state, but after 4-6 min. During the third session of "animal hypnosis," the course of electrical activity in the alpha and beta rhythms in the premotor and sensorimotor areas of the cortex became wave-like in nature.

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Reflection of cortical waves of spreading depression in changes in high-frequency gamma activity was shown to improve significantly in conditions of bipolar recording of brain electrical activity. Intense suppression of the EEG gamma range (37-47 Hz) was seen in all cortical areas studied at the moment of onset of waves of spreading depression. The drop in the power of EEG gamma activity had clear leading and trailing fronts, allowing the passage time of the wave to be evaluated in each cortical area, as well as the sequence of propagation. Waves of spreading depression were characterized by normal, i.e., sequential movements across the cortex, only in the first 3-4 experiments. When experiments were continued, there were changes in the latent period and distortions of the propagation sequence. In some cases, waves of spreading depression responded to standard injections of KCl by developing rapidly (0.5-2 min) over the whole of the dorsal surface of the neocortex. More frequently, the wave was delayed (to 6-9 min) was completely blocked in some areas of the cortex. Different types of mild convulsive activity could accompany both the rapid propagation of waves across the cortex and inhibition of wave development. In most cases, there were no electrophysiological signs of changes in neocortical excitability. However, alterations to the spatial characteristics of waves of spreading depression and the spontaneous appearance of repeated waves provided evidence of changes in the functional state of the brain. Overall, EEG spectral analysis in conscious rabbits allowed analysis of spreading depression both in cases of sequential propagation across the cortex and in cases of atypical modes of development of this phenomenon.